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Doppler system looks inside engines

22 Oct 2002

Japanese researchers build a laser Doppler velocimetry system that analyzes flow conditions inside combustion engines.

Researchers in Japan have built a laser Doppler velocimetry (LDV) system specifically tailored for analyzing flow conditions inside a practical combustion engine.

The fiber-LDV probe plugs directly into an engine's sparkplug port, requiring no structural modifications to the engine. Engines are usually adapted to accommodate optical access by introducing a window. However, this modification limits the maximum speed of the engine to 1500 rpm or less, whereas a practical engine typically operates at over 5000 rpm.

Tsuyoshi Nakajima and colleagues at Kobe University developed the plug-in system. They presented it at the 11th International Symposium on Applications of Laser Techniques to Fluid Mechanics in Lisbon last July, having used it to study flow velocities and turbulence intensity in a standard 1500 cc four-stroke car engine made by Subaru. The probe operated with the engine running in typical motoring conditions, with all four cylinders investigated.

The fiber-LDV system is based on an argon-ion laser operating at 514.5 nm. The engine flow was seeded with particles of silicon oil and a burst spectrum analyzer collected the Doppler signals.

Nakajima and colleagues conclude that the fiber-LDV can be used in engine design to improve the cylinder, intake port and valve system.

Author
Michael Hatcher is technology editor of Opto and Laser Europe magazine.

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